1. Field of the Invention
The invention relates to an arrangement for detecting the angle of rotation of a rotatable element, in which, while evaluating properties of a sensor arrangement which can be magnetically influenced, a first magnetic field generated or influenced by the rotatable element is detectable and can be used for determining the angle of rotation, the sensor arrangement comprising a plurality of magnetic field-sensitive sensor elements which are substantially planar and are substantially arranged in one plane, which sensor elements are connected to at least two bridge circuits each supplying a signal assigned to a function of the angle of rotation, whereby the sensor arrangement is adapted to supply signals which are unambiguously assignable to a direction of the first magnetic field via a first angular range, means for supplying a magnetic auxiliary field to the sensor arrangement, by means of which a modification of the signals assignable to the direction of the first magnetic field can be achieved for unambiguous assignment of an angle via a second angular range, the means for applying the magnetic auxiliary field to the sensor arrangement comprising a substantially planar coil arranged with its planar extension along the planar arrangement of the sensor elements.
2. Background Art
An arrangement for detecting the angle of rotation of a rotatable element is known from DE 198 39 446 A1, in which, while evaluating properties of a sensor arrangement which can be magnetically influenced, a first magnetic field generated or influenced by a rotatable element is detectable in an evaluation circuit and can be used for determining the angle of rotation. According to the publication of DE 198 39 446 A1, the sensor arrangement supplies signals which are unambiguously assignable to a direction of the first magnetic field via a first angular range, particularly an angular range of 180xc2x0, while utilizing the magnetoresistive effect. Furthermore, means for applying a magnetic auxiliary field to the sensor arrangement are provided, by means of which a modification of the signals assignable to the direction of the first magnetic field can be achieved for unambiguous assignment of an angle via a second angular range, particularly 360xc2x0.
As is evident from FIG. 3 and its associated description in this document, the means for applying a magnetic auxiliary field to the sensor arrangement comprise a thin-layer planar coil which is insulated by a non-conducting intermediate layer and is arranged via AMR resistors in two Wheatstone bridges, which constitute the sensor arrangement. The planar coil consists of two spatially separated parts each extending via a spatially juxtaposed configuration of given AMR resistors in the two Wheatstone bridges.
This arrangement has a very large surface area. It therefore requires very large component substrates in addition to the construction mentioned in DE 198 39 446 A1. Due to the large-area structure of the planar coil, a high sensitivity to magnetic interference fields results. For a monolithic integration and miniaturization of such an arrangement, its large-area construction is also a drawback.
An angle sensor with at least two touchlessly measuring sensor units arranged in an angularly offset configuration is known from EP 0 671 605 A2, whose sensor voltages have similar but angularly offset, sinusoidal functions (sensor characteristic) of the angle a to be measured with respect to a rotatable element. This angle sensor is arranged on a chip and comprises two sensor units with bridge elements which are interleaved in such a way that a bridge element of the one sensor element is each time followed by a bridge element of the other sensor unit with a 45% spatial offset around a common center. An evaluation circuit coupled to the bridge elements can unambiguously generate an angle sensor voltage constituting a measure for the angle a via an angular range of up to 180xc2x0.
It is an object of the invention to form an arrangement of the type described in the opening paragraph in such a way that an unambiguous measurement through a large angular range, preferably up to 360xc2x0 is possible with a compact, simple and low-cost arrangement.
According to the invention, in an arrangement for detecting the angle of rotation of a rotatable element, as described in the opening paragraph, this object is achieved in that the sensor elements of each bridge circuit are arranged in a star-shaped configuration, in that the sensor elements of the different bridge circuits are interleaved in a star-shaped concentric manner, and in that the substantially planar coil comprises a substantially spirally concentric, planar winding along its planar extension.
Due to the combination of the compact angle sensor unit with a planar coil which is formed in a very simple manner, a very simple and compact unit with only one simple sensor arrangement is obtained which can be easily manufactured at low cost, is suitable for miniaturization and has a low sensitivity to interference.
In this respect it is to be noted that the description of DE 198 39 446 A1 gives an indication that the generation of an auxiliary field by a planar coil of the type described in this document is also possible in an alternative arrangement of the AMR resistors in accordance with the star-shaped interleaved configuration described in EP 0 671 605 A2. The construction of the planar coil shown in DE 198 39 446 A1 does not, however, yield a useful result in combination with the arrangement of the AMR resistors in accordance with the star-shaped interleaved configuration described in EP 0 671 605 A2. A stimulus for constructing the planar coil in the way as described in the present invention is not given and is neither further detailed in this document.
A very advantageous embodiment of the arrangement according to the invention is characterized in that the substantially spirally concentric planar winding of the substantially planar coil and the sensor arrangement constituted by the substantially star-shaped concentrically interleaved sensor elements at least substantially coincide by way of their centers. This results in a very compact construction with a minimal surface area.
In the arrangement according to the invention, it is not necessary to generate a homogeneous magnetic field in the plane in which the sensor elements are arranged. In contrast, it is sufficient to give the magnetic field a defined direction. In accordance with another advantageous embodiment of the invention this can be effected in a simple way in that the substantially spirally concentric planar winding of the substantially planar coil and the sensor arrangement constituted by the substantially star-shaped concentrically interleaved sensor elements are arranged eccentrically to each other by a predetermined extent. As a result, a preferred direction of the magnetic field is adjusted in the plane of the sensor elements. For this eccentric arrangement, a slightly larger surface area as compared with the concentric arrangement is of course necessary.
For an at least substantially concentric arrangement of the planar coil with respect to the sensor arrangement, it is advantageous and useful when, in accordance with a further embodiment of the invention, signals which are only generated by half bridges of the bridge circuits are utilized for evaluating the sensor arrangement properties which can be magnetically influenced for detecting the angle of rotation of the rotatable element. By taking the signals only from half bridges, it can be achieved that possibly only one direction of the magnetic auxiliary field is used for the evaluation of the signals supplied by the sensor arrangement.
In the arrangement according to the invention, the substantially planar coil is preferably integrated monolithically on the sensor arrangement. This manufacturing mode allows a very low-cost and precise manufacture of a very compact structure. The manufacture of the substantially planar coil can thereby be combined with that of the sensor arrangement in a joint manufacturing process.
Arrangements of the type according to the invention are used in all ranges in which simple, low-cost, compact and robust sensors are needed for large angular ranges. A preferred field of use is in the automobile technique but also, for example, for replacing sliding potentiometers by contactless rotation angle sensors in electrotechnical and electronic fields.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.